Cryptic introduction of the red alga Polysiphonia morrowii Harvey (Rhodomelaceae, Rhodophyta) in the North Atlantic Ocean highlighted by a DNA barcoding approach

Macroalgae are prone to be introduced outside of their autochthonous area; however, the difficulty to unequivocally identify them based on morpho-anatomical features, mainly due to the lack of diagnostic characters, often hampered the rapid detection of exogenous species. In the present study, we document that the Polysiphonia species that dominates, during spring, the high intertidal level in Brittany is Polysiphonia morrowii. We demonstrated the presence of this alien species in the North Eastern Atlantic in light of molecular sequences. This species originally from the Northwest Pacific Ocean has already been reported as introduced in Chile and New Zealand on a molecular ground and has been suspected in North Sea and Mediterranean Sea based on morpho-anatomical ground. Among the 105 individuals of P. morrowii collected along the coast of Brittany, three haplotypes were found suggesting several introduction events. In our opinion, the progression of this exogenous species, which has been so far undetected due to its morphological similarities with native species, should be further monitored.

► A barcoding approach revealed the presence of alien species along Brittany coast. ► Polysiphonia morrowii share morphological characters with native species. ► Cryptic introduction overlooked.